xen/balloon: pre-allocate p2m entries for ballooned pages

Pages returned by alloc_xenballooned_pages() will be used for grant
mapping which will call set_phys_to_machine() (in PV guests).

Ballooned pages are set as INVALID_P2M_ENTRY in the p2m and thus may
be using the (shared) missing tables and a subsequent
set_phys_to_machine() will need to allocate new tables.

Since the grant mapping may be done from a context that cannot sleep,
the p2m entries must already be allocated.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 25fd1bd949d8..f56662324a47 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -602,6 +602,11 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
                 page = balloon_retrieve(true);
                 if (page) {
                         pages[pgno++] = page;
+#ifdef CONFIG_XEN_HAVE_PVMMU
+                        ret = xen_alloc_p2m_entry(page_to_pfn(page));
+                        if (ret < 0)
+                                goto out_undo;
+#endif
                 } else {
                         ret = add_ballooned_pages(nr_pages - pgno);
                         if (ret < 0)